You next best low budget choie is a good BBC mechanical flat tappet cam and lifters.
They work real good too.
The BBC street hyd rollers tend to give up the ghost at 5500ish rpm some as soon as 5200
some 5800. most all al giveing up power by 6000rpm.
You do not want that with nitrous. The new improved limited plunger travel hyd roller lifters Crane etc.
are pricey and require a real good cam lobe design (Crane Hyd roller) and big springs.
now you are into money.
a lot of people that have been down this road end up running a solid mechanical roller lifter and more spring
on their Hyd roller cam to get the nessessary rpm capability . (very small cold lash setting .001" to .004")
Why not get get the right mechanical street roller cam and mechanical roller lifters in the first place?
Do you got enough money to do this twice- three times?
The mech street roller is the good deal ..... net cost and far superior performance in a BBC.
The XR mechanical street roller K kits are hard to beat.